When conventional resists composed of a novolak resin and a naphthoquinonediazide compound are used for pattern formation by lithography using far ultraviolet rays or excimer laser rays, strong absorption of these rays by the novolak resin and the naphthoquinonediazide compound in the far ultraviolet region prevents the rays from reaching the bottoms of the resist, resulting in low sensitivity and formation of tapered patterns.
One of means for solving these problems is a chemically amplified resist composition described in U.S. Pat. No. 4,491,628, European Patent 249,139, and so forth. The chemically amplified positive resist composition is a pattern forming material, in which irradiation with a radiation such as far ultraviolet rays causes the formation of an acid in exposed areas, a reaction where the acid functions as a catalyst makes the difference of solubility in a developer between irradiated areas and unirradiated areas, thereby leading to the formation of a pattern on a substrate.
Examples of such a material include a combination of a compound generating an acid by the photolysis thereof with an acetal or an O,N-acetal compound described in JP-A-48-89003 (The term "JP-A" as used herein means an "unexamined published Japanese patent application); a combination of the acid-generating compound with an orthoester or an amidoacetal compound described in JP-A-51-120714; a combination of the acid-generating compound with a polymer having an acetal or a ketal group in the main chain thereof described in JP-A-53-133429; a combination of the acid-generating compound with an enol ether compound described in JP-A-55-12995; a combination of the acid-generating compound with an N-acylimino carbonate compound described in JP-A-55-126236; a combination of the acid-generating compound with a polymer having an orthoester group in the main chain thereof described in JP-A-56-17345; a combination of the acid-generating compound with a tert-alkyl ester compound described in JP-A-60-3625; a combination of the acid-generating compound with a silyl ester compound described in JP-A-60-10247; and a combination of the acid-generating compound with a silyl ether compound described in JP-A-60-37549 and JP-A-60-121446. In principle, these compositions exhibit high sensitivity, because of quantum yields exceeding 1.
Similarly, a system which decomposes by heating in the presence of an acid to become soluble in alkali, although the system is stable in time elapsing at room temperature, include a combination of a compound generating an acid by exposure with an ester or a carbonate compound having a tertiary or secondary carbon (for example, tert-butyl and 2-cyclohexenyl) as described in JP-A-59-45439, JP-A-60-3625, JP-A-62-229242, JP-A-63-27829, JP-A-63-36240, JP-63-250642, Polym. Eng. Sce., vol.23, p.1012 (1983), ACS. Sym., vol.242, p.11 (1984), Semiconductor World, November, 1987, p.91, Macromolecules, vol.21, p.1475 (1988), SPIE, vol.920, p.42 (1988), and so forth. This system also exhibits high sensitivity and can be effective for the above-mentioned light sources of shorter wavelengths, because the system has weaker absorption than the naphthoquinonediazide/novolak resin system in the deep ultraviolet region.
The above-mentioned chemically amplified positive resist compositions can be roughly divided into two systems, that is, a three component system comprising an alkali-soluble resin, a compound which generates an acid by irradiation with an active ray or radiation (photo-acid generator), and a dissolution inhibitive compound acting on an alkali-soluble resin containing an acid-decomposable group and a two component system comprising a resin having a group which decomposes by a reaction with an acid to become soluble in alkali and a photo-acid generator.
For example, a photosensitive composition which contains a compound having a C--O--C or C--O--Si bond decomposing by the action of an acid, a photo-acid generator, an alkali-soluble resin, and a certain amount of an amine or amide compound is described in WO94/01805; a radiation-sensitive resin composition which contains an alkali-soluble resin, a radiation-sensitive acid-forming agent, a dissolution inhibitive compound acting on an alkali-soluble resin having an acid-decomposable group, and further, a nitrogen-containing basic compound is described in JP-A-5-232706; and a positive photosensitive composition which contains a tert-alkyl ester group-containing low molecular weight compound having a molecular weight of 3,000 or less and increasing in solubility in an alkali aqueous solution by the action of an acid, a polyhydroxystyrene resin, and a photo-acid generator is described in JP-A-6-242608.
However, these compositions have the disadvantages of sensitivity decrease, T-top formation and narrowed line width which are caused from exposure to post exposure bake.